The present invention relates to an airtight external shroud for a turbine wheel of a turbomachine such as an airplane turbojet or turboprop engine.
A turbomachine turbine comprises several stages each involving a nozzle assembly formed of an annular row of stationary vanes borne by a casing of the turbine, and a wheel mounted such that it can rotate downstream of the nozzle assembly in a cylindrical or frustoconical shroud formed by ring sectors which are positioned circumferentially end to end and are attached to the casing of the turbine.
Each ring sector comprises a circumferentially directed plate which bears a block of abradable material fixed to the internal surface of the plate. This block is, for example, of the honeycomb type and is intended to become worn by rubbing against the external periphery of the wheel in order to minimize the radial clearances between the wheel and the ring sectors.